This invention generally relates to electronic devices or components comprising a ceramic body and end terminations having a good absorbant effect against heat shock on soldering as well as a good solderability on connecting a conducting wire, and particularly relates to ones having an end termination comprising a metal phase as an electrical conducting component and an inorganic glass phase as a bonding component for adhesion to the ceramic body.
This invention also relates to a method for forming an end termination at very low cost as well as a paste composition for forming same.
Recently, with developments in on the miniaturization and high densification of circuits, most of electronic devices and components have been generally mounted on the surfaces of base plates. Among these devices and components, electronic components such as solid resistant elements and multi-layer ceramic capacitors are provided with end terminations, which are mounted on the ends of ceramic bodies by bonding a sintered metallic powder product thereto with glass frit. This arrangement is called a metal glazing type one.
As this end termination portion is soldered directly on a patching metal surface of circuit base plate, it is required to have a good wettability with solder and prevent from occurring an absorbing phenomenon by solder wherein a metal phase of the end termination portion can be absorbed and swept away by means of contacting a melting solder.
As the end termination, there has been conventionally used a silver electrode which can be sintered in air. For solving the above problems, there are now proposed to use an Ag-Pd alloy electrode in place of the silver electrode and also to cover a sintered silver end termination at outer surface by a Ni coating and further cover it by a Sn-Pb coating (solder plating). However, it is disadvantageous that use of this method make a productivity of the end termination worse and thus makes production cost thereof high.
Furthermore, when a solder melt contacts an end termination of an electronic component on soldering it on a patch board, cracks have been sometimes occurred at the end termination owing to a large tension thereon caused by a temperature difference between the ceramic body of the component and the end termination adhered thereto and thus by a heat expansion difference therebetween. According to demand, therefore, it has been required to preheat the component in order to avoid generation of such a big temperature difference on soldering.
Meanwhile, for decreasing the cost of production, it is requested to use a base metal such as Cu, Ni and so on as end termination materials in place of silver. In multi-layered capacitors, provided with internal electrodes made of the base metal, which is subjected to a sintering treatment under an atmosphere containing a low partial oxygen pressure, it has been already proposed as described in U.S. Pat. No.3,920,781 to use an end termination made of a base metal such as Ni and Cu. These base metals have a poor absorption phenomenon as above, but have a problem in solderability, especially in a lowering of wettability owing to surface oxidation of the end termination. Therefore, it has been proposed to subject outer surface of the end termination to a solder plating. Also, according to demand, it has been attempted to subject the component to a preheat treatment in order to avoid generation of cracks as in the conventional case.
The above plating method is not advantageous since the requirement of additional steps for plating makes manufacturing process complicated and also the electronic components expensive. Furthermore, in some case, a dipping treatment of the component in a plating liquid may change and deteriorate its chemical and physical properties. The plating method also has no effect for avoiding generation of crack in the component under soldering.